Abstract
Because of their quantum fluctuations, axion fields had a chance to experience field excursions traversing many minima of their potentials during inflation. We study this situation by analyzing the dynamics of an axion field , present during inflation, with a periodic potential given by . By assuming that the vacuum expectation value of the field is stabilized at one of its minima, say, , we compute every -point correlation function of up to first order in using the in-in formalism. This computation allows us to identify the distribution function describing the probability of measuring at a particular amplitude during inflation. Because is able to tunnel between the barriers of the potential, we find that the probability distribution function consists of a non-Gaussian multimodal distribution such that the probability of measuring at a minimum of different from increases with time. As a result, at the end of inflation, different patches of the Universe are characterized by different values of the axion field amplitude, leading to important cosmological phenomenology: (a) Isocurvature fluctuations induced by the axion at the end of inflation could be highly non-Gaussian. (b) If the axion defines the strength of standard model couplings, then one is led to a concrete realization of the multiverse. (c) If the axion corresponds to dark matter, one is led to the possibility that, within our observable Universe, dark matter started with a nontrivial initial condition, implying novel signatures for future surveys.
- Received 1 February 2017
DOI:https://doi.org/10.1103/PhysRevD.96.023530
© 2017 American Physical Society